Microprocessor controlled photocomposition systems and other printers are used to set up and edit text to be printed as books, magazines, pamphlets, or otherwise. Such systems need to combine the capabilities of word processing to provide for ease of entry and revision along with the more sophisticated abilities to automatically select multiple fonts of varying type size and orientation. Because photocomposition systems require access to many fonts and are not limited to a single character type as in word processing, much system complexity is directed toward the ability to handle many fonts quickly and efficiently.
Photocomposition systems must deal with a large variety of fonts and sizes. The storage of data representing the fonts, the process of accessing selected font characters and the process of displaying them rapidly in response to keyboard operator selection, without using enormous amounts of expensive memory and processing capability, places a difficult demand upon photocomposition system design. In addition, because of the editing flexibility required for a photocomposition system, characters being set up on the display will frequently overlap adjacent characters. Thus, adding or editing a character in such an overlapping arrangement can readily lead to destructive interference with existing characters as each new character is added to the display. This, of course, will yield intolerable output results, so a great deal of complexity may be required in the system in order to avoid such interference.